The \(X(3940)\)  was first observed by the Belle Collaboration in
\(e^+e^-\rightarrow J/\psi +X\)  [1]}. This state is also established in
the invariant mass spectrum of \(D^*\bar{D}\)  in
\(e^+e^-\rightarrow J/\psi D^*\bar{D}\)  process [2]}. The updated mass and width
of \(X(3940)\)  are \(M=3942^{+7}_{-6}\pm 6\)  MeV and \(\Gamma =37^{+26}_{-15}\pm 8\)  MeV, respectively.
Its decay into \(DD^*\)  but not \(DD\)  suggests that
it has unnatural parity. The most likely interpretation of \(X(3940)\)  is that it
is the \(\eta _c(3S)\)  state with \(J^{PC}=0^{-+}\)  [3]}, although the predicted
mass in potential models appears to be higher than the observations.
